1. Field of the invention
The present invention relates to an apparatus for performing epitaxial growth of a compound semiconductor crystal from liquid phase (hereinafter to be referred to as "solution growth"), and more particularly it pertains to an apparatus for performing a solution growth of a compound semiconductor crystal relying on the temperature difference technique.
2. Description of the prior art
Group III-V compound semiconductor crystals as represented typically by GaAs, and Group II-VI compound semiconductor crystals known typically by, for example, ZnS are being used widely as the materials for manufacturing various semiconductor devices such as laser diodes (LDs) and light-emitting diodes (LEDs).
Compound semiconductor crystals which are used in these semiconductor devices are obtained usually through epitaxial growth in liquid phase, i.e. through solution growth.
The method for performing such solution growth of compound semiconductor crystals which has been introduced in this field of technology in the past and is widely known was developed by RCA Corporation of U.S.A. and is known as "Nelson method".
This known method uses a solution of a certain metal serving as a solvent in which a desired compound semiconductor material is dissolved up to the saturated condition, which will hereinafter be referred to simply as a "melt", and in the state of this melt that a predetermined compound semiconductor crystal which will serve as a substrate is in contact therewith, the melt is cooled down slowly, so that, owing to the lowering of the temperature of the melt, the supersaturated compound semiconductor material is epitaxially grown as a crystal on the substrate.
In this known method, the growth of crystal proceeds during a cooling process, and accordingly there is performed only one growth of crystal for one process of growth. Thus, this known method is not available for mass production of crystal. Furthermore, when the layer which is grown according to this method is viewed in the direction of its thickness, there develops difference in the amount of the content of the impurity at various sites of this grown layer owing to the difference in the temperature of the growth occurring at these various sites. Thus, in the growth of a mixed crystal, the composition of the crystal will exhibit variance in the direction of the thickness of the grown layer. Also, it has been made clear that imperfection of crystal is induced also owing to the changes in temperature during the growth. In spite of these various drawbacks of this known method, a crystal growth can be effected with a relative easiness, and therefore, this Nelson method is being widely employed in this field of technology.